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The best examples in the geologic record of rapid (1-k.y. to 1-m.y. timescale) wholesale extinctions linked to massive perturbations of the global carbon cycle and extreme changes in Earth's climate come from the Cretaceous and Paleogene Periods (e.g., oceanic anoxic events [OAEs] and the Late Paleocene Thermal Maximum [LPTM]). Little is known about the underlying causes and effects of these critical events in Earth history, however. To a significant extent, these gaps in our understanding arise because of a lack of modern high-resolution paleoceanographic records from ocean drill sites, particularly from the tropics, that are so important in driving global ocean-atmospheric circulation. Deep ocean drilling can access expanded sections of Cretaceous- and Paleogene-age deep-sea sediments on the Demerara Rise (Fig. F1), fulfilling priorities of the Ocean Drilling Program (ODP) Extreme Climates Program Planning Group and Long Range Plan. The Demerara Rise represents an ideal drilling target for this purpose because the target sediments (1) crop out on the seafloor, (2) exist with good stratigraphic control in expanded unlithified sections, (3) contain spectacularly well-preserved microfossils, and (4) were deposited within the core of the tropics in a proximal location to the equatorial Atlantic gateway.

Four primary drill sites (with six alternate sites) have been selected on the northern margin of Demerara Rise (Figs. F1, F2, F3). The sites are located in a depth transect (present water depths of 1895–3215 m) along a grid of high-resolution multichannel seismic reflection lines supplemented by existing industry lines (Fig. F2), with stratigraphic control from Deep Sea Drilling Project (DSDP) Site 144, industry well Demerara A2-1, and gravity cores of Paleogene sediments from Meteor cruise 49/4.

DSDP Site 144 was spot cored toward the escarpment in a highly condensed section. Yet even here, Demerara Rise preserves a highly expanded (~150 m thick) sequence of dark clays and shales correlative to at least three Cretaceous OAEs plus a further 150-m-thick sequence of upper Paleocene to lower Oligocene carbonate ooze. These sections thicken inboard, and records of at least five OAEs (OAE-1b, -1c, -1d, -2, and -3) can probably be penetrated by transect drilling on the Demerara Rise with good potential for the LPTM and Eocene/Oligocene boundary. The proposed transect of Cretaceous and Paleogene cores will be used to evaluate, at high resolution, the following:

  1. The history of multiple Cretaeous OAEs in an equatorial setting and thereby test competing hypotheses for their causes and climatological effects (particularly in relation to rapid emission and draw-down of greenhouse gases);
  2. The detailed response of oceanic biotic communities across a range of paleowater depths to extreme perturbations in the geochemical carbon cycle and global climate;
  3. Short- and long-term changes in greenhouse forcing and tropical sea-surface temperature response;
  4. Key Paleogene events of biotic turnover and/or inferred climate extremes, particularly the LPTM and the Eocene/Oligocene boundary; and
  5. The role of equatorial Atlantic gateway opening in controlling paleoceanographic circulation patterns, OAEs, and cross-equatorial ocean heat transport into the North Atlantic.

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